1. Field of the Invention
The present invention relates to a potential measuring device which measures a surface potential of a charged object in a non-contact manner.
2. Description of the Related Art
To measure a surface potential of a charged object which is charged with an electric charge, a potential measuring device of non-contact type is used, with which measurement is performed under the condition that a measuring element is not contacted with the charged object. Among such potential measuring devices, there is one described in Patent Document 1 for example. The potential measuring device of the type described in Patent Document 1 includes a pair of vibrating pieces, an electromagnetic coil, and a piezoelectric element. A chopper electrode is provided on a tip side of the pair of vibrating pieces, and this chopper electrode is located between the charged object and a detecting electrode. Then, when the pair of vibrating pieces is vibrated by operation of the electromagnetic coil and the piezoelectric element, the chopper electrode changes electric flux lines between the charged object and the detecting electrode. Thus, an alternating voltage is generated on the detecting electrode, to thereby enable measurement of the surface potential.    [Patent Document 1] Japanese Patent Application Laid-open No. H10-115647
In the potential measuring device of the type described in Patent Document 1, the electromagnetic coil is often attached in close vicinity to one of the pair of vibrating pieces, for example. In this case, there is created a state that respective natural frequencies of the vibrating pieces do not match. In such a state that the natural frequencies of the vibrating pieces do not match, the amplitude of the chopper electrode cannot be made large, and thus good sensitivity cannot be obtained.
The present invention is made based on the above-described situation, and an object thereof is to provide a potential measuring device of non-contact type which has higher measurement sensitivity than conventional ones.